1. Field of the Invention
The present invention relates to a motor. In particular, the present invention relates to a brushless D.C. motor.
2. Description of the Related Art
A computer generally not only requires a suitable ambient temperature but also requires timely expelling of heat generated by the electronic elements of the computer during operation so as to keep the electric circuits of the computer stable. To this end, a brushless D.C. motor having a power not greater than 3W is usually mounted inside the main casing of a personal computer for expelling heat generated by the electronic elements in the main casing. Due to the advantages of small size, few parts, light weight, and large air output, such a brushless D.C. motor is not only widely used in computers but also in other electronic products that requires heat dissipation. Currently, the rotor of a brushless D.C. motor is supported by an oily bearing which has the advantages of simple structure, easy manufacture, low cost, and excellent lubrication. Since the overall weight of the rotor is supported by the bearing that does not turn, when the rotor shaft is located in a horizontal plane, the lower side wall of the hole of the oily bearing receiving the rotor shaft is subject to force. As a result, the lower side wall is worn and becomes ellipsoid after a period of time, and rotation of the rotor shaft would not be smooth. Noise is generated, and the life of the motor is shortened. Unfortunately, the shaft of the brushless D.C. motor used in electronic products lies in a horizontal plane, and the wear due to gravity of the shaft is inevitable to the oily bearing. The noise is extremely annoying if it is used in a portable electronic device such as a portable computer (or so-called xe2x80x9cnotebookxe2x80x9d) or testing equipment. In order to prevent generation of noise, the oily bearing includes an O-ring and a washer in each of two ends thereof. However, such a structure causes an obstruction to timely expelling of the gas generated as a result of friction of the rotor shaft at high speed and the wall of the hole of the bearing receiving the rotor shaft. Thus, the gas solidifies into nitride that blocks the gap between the rotor shaft and the bearing. The friction is increased, and the life of the motor is further shortened. Roller bearings mounted on two ends of the rotor shaft have been proposed to solve the problem of the offset wear of the oily bearing resulting from offset load and the noise resulting from the wear, and the performance was proved excellent. However, the roller bearings are more expensive than the oily bearings, and the installation of the roller bearings are not easy. The cost is thus high. In addition, the bearings have a poor cushioning effect to mechanical vibrations. The offset load to the bearings is not completely eliminated such that offset wear may still occur.
It is the primary object of the present invention to provide a magnetic shaft for a brushless D.C. motor to mitigate and/or obviate the offset wear of the bearing resulting from the weight of the rotor, to improve the cushioning ability for absorbing the mechanical vibrations, and to reduce the cost for production.
A brushless D.C. motor in accordance with the present invention comprises a casing, a bearing, a stator, and a rotor having a shaft. The bearing is mounted to an end of the shaft. A first magnetic member is mounted on an inner side of the casing. A second magnetic member is formed on the other end of the shaft and faces and is spaced from the first magnetic member. The shaft floats on an axis by magnetic force provided by the first and second magnetic members to thereby reduce the load to the bearing. Thus, the frictional resistance is low, and rotation of the motor is smooth with a low noise. The motor is shock-resistant and has a long life. Thus, the motor is particularly suitable for portable electronic products.
Other objects, specific advantages, and novel features of the invention will become more apparent from the following detailed description and preferable embodiments when taken in conjunction with the accompanying drawings.